A continuing study of the causes for interindividual variation in pharmacokinetics of the drugs in dogs and humans. Work will continue with propranolol utilizing a stereospecific assay to monitor the intact drug and its metabolites and to evaluate the effect of disease states on changes in metabolism. Studies in dogs and then in humans are to be initiated on erythromycin with a specific high pressure liquid chromatographic assay to monitor intact drug and metabolites. The drug will be administered to a special dog model which will allow a separate study to gut degradation, gut wall metabolism and liver first-pass metabolism and to determine how they affect the rate and extent of absorption of the drug.